It is the purpose of this study to resolve the cold resistant nature of the brain of a mammlian hibernator. The topics of interest and investigation are: (1) Electrolyte metabolism, primarily that associated with Na ion and K ion balance, energy transduction in biomembranes, (2) membrane lipid turnover, (3) membrane biogenesis. The use of a hibernating species of mammal, the hamster, is employed in these studies, since it can alter naturally when cold exposed, both the chemical and physical nature of its neural elements.